Our studies of surgically commissurotomized patients involve extensive pre and post operative testing at various levels of neurological, cognitive and intellectual functioning. In addition, we are continuing to assess the nonverbal cognitive functioning of patients sustaining vascular lesions to the left hemisphere rendering them aphasic. Our studies of nonhuman primates focus on the cognitive cost of commissurotomy as well as basic issues in sensory-motor integration. In addition, we are beginning to explore some of the neuroanatomical substrates of interhemispheric integration which have not previously been investigated.